The present invention relates to a fluid controller of the type used to control the flow of fluid from a source of pressurized fluid to a fluid pressure operated device, such as a vehicle steering cylinder.
A typical fluid controller of the type to which the present invention relates includes a housing which defines various fluid ports, and further includes a fluid meter, a primary valve member, a follow-up valve member, and an arrangement for imparting follow-up movement to the follow-up valve member in accordance with the fluid flow through the fluid meter. The flow through the controller valving is directly proportional to the area of the main variable flow control orifice which, in turn, is proportional to the relative displacement between the primary and follow-up valve members.
In conventional fluid controllers of the type described above, the primary valve member has been rotatable, and the follow-up valve member has been relatively rotatable, with the various flow control orifices being defined by the overlap of passages and ports defined by the primary and follow-up valve members, respectively, as the primary valve member is rotated, relative to the follow-up valve member.
Although fluid controllers of the type described above have been satisfactory in operation, and very successful commercially, there are inherent drawbacks to fluid controllers of that type. Typical spool-sleeve fluid controllers which define variable flow control orifices in response to relative rotation of the spool and sleeve typically require that the spool include a substantial number of axially-extending milled slots or passageways on the surface of the spool, thus adding to the cost and complexity of the manufacturing process. In addition, it is more difficult in such controllers to provide suitable pressure balancing of the sleeve, to prevent it from clamping onto the outer surface of the spool, in a region where the sleeve is surrounded by pressurized fluid, for example, in an annular chamber defined by the housing.